The expression “hatch” is to be understood in a broad sense. Those hatches include tail gates, boot lids, engine bonnets, doors, in particular side doors, load-space floors or the like of a motor vehicle.
The drive device in question has gained increasing importance in the last years in order to provide a high level of comfort for the user. This is especially true for large hatches of a motor vehicle, which weight make it hard to manually perform an opening motion or a closing motion of the hatch.
In a first alternative known from the state of the art the drive device is at least partly motor driven and accordingly comprises an electric motor and a gear mechanism to generate a bidirectional drive motion. Here, a spring arrangement supports the electric motor, as shown in US 2011/271595 A1 for an example. A certain damping of the drive motion is provided by the friction inside the drive train of the drive device.
In a second alternative known from the state of the art the drive device is solely spring driven and serves as a support of the hatch against the forces of gravity. Such drive device normally comprises a spring arrangement and a damping arrangement in the design of a gas damper, which is a comparably costly setup for an only spring driven device. In most cases such a drive device generates a drive motion in an opening direction of the hatch only.
In both above noted alternatives of known drive devices a spring arrangement is integrated into the drive device, which spring arrangement provides spring forces of considerable magnitude. Those high spring forces generally include a risk of material damage or even the injury of persons.
If, for example, the connection between the drive device and the hatch breaks, the spring arrangement could relax impulse like caused by its high spring forces leading to an enormous impact when reaching an end position of the drive device. The resulting impact energy may be high enough to break the structure of the drive device, possibly freeing the spring arrangement with a resulting risk of damage.
Another risky situation can arise when the hatch is being opened manually by a user with extreme opening forces and correspondingly opening speeds. In such a misuse situation the above noted, high impact energy is generated when reaching the respective end position of the hatch, again leading to the risk of damage.
In order to guarantee a sufficient operational safety, the above noted, risky situations require an effective and systematic damping especially of those drive motions, that are taking place with exceptionally high speeds. With the known approaches this leads to a costly setup of the respective drive device.
It is the object of the invention to improve the known drive devices such that a high operational safety may be realized with low costs.